package org.apache.lucene.search.spans;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.util.Collection;

/** Expert: an enumeration of span matches.  Used to implement span searching.
 * Each span represents a range of term positions within a document.  Matches
 * are enumerated in order, by increasing document number, within that by
 * increasing start position and finally by increasing end position. */
public abstract class Spans {
    /** Move to the next match, returning true iff any such exists. */
    public abstract boolean next() throws IOException;

    /** Skips to the first match beyond the current, whose document number is
     * greater than or equal to <i>target</i>. <p>Returns true iff there is such
     * a match.  <p>Behaves as if written: <pre>
     *   boolean skipTo(int target) {
     *     do {
     *       if (!next())
     * 	     return false;
     *     } while (target > doc());
     *     return true;
     *   }
     * </pre>
     * Most implementations are considerably more efficient than that.
     */
    public abstract boolean skipTo(int target) throws IOException;

    /** Returns the document number of the current match.  Initially invalid. */
    public abstract int doc();

    /** Returns the start position of the current match.  Initially invalid. */
    public abstract int start();

    /** Returns the end position of the current match.  Initially invalid. */
    public abstract int end();

    /**
     * Returns the payload data for the current span.
     * This is invalid until {@link #next()} is called for
     * the first time.
     * This method must not be called more than once after each call
     * of {@link #next()}. However, most payloads are loaded lazily,
     * so if the payload data for the current position is not needed,
     * this method may not be called at all for performance reasons. An ordered
     * SpanQuery does not lazy load, so if you have payloads in your index and
     * you do not want ordered SpanNearQuerys to collect payloads, you can
     * disable collection with a constructor option.<br>
     * <br>
    * Note that the return type is a collection, thus the ordering should not be relied upon.
    * <br/>
     * @lucene.experimental
     *
     * @return a List of byte arrays containing the data of this payload, otherwise null if isPayloadAvailable is false
     * @throws java.io.IOException
    */
    // TODO: Remove warning after API has been finalized
    public abstract Collection<byte[]> getPayload() throws IOException;

    /**
     * Checks if a payload can be loaded at this position.
     * <p/>
     * Payloads can only be loaded once per call to
     * {@link #next()}.
     *
     * @return true if there is a payload available at this position that can be loaded
     */
    public abstract boolean isPayloadAvailable();

}
